1. Field of the Invention
The present invention relates generally to the field of ophthalmology. In particular, the invention relates to the treatment of glaucoma and ocular hypertension using a combination of at least one clonidine derivative (e.g., para-amino clonidine) and at least one prostaglandin.
2. Discussion of Related Art
Although the underlying causes of glaucoma are not understood, its symptoms often include elevated intraocular pressure, which may be caused either by over-production of aqueous humor or by inadequate outflow of aqueous humor. If left untreated, or if inadequately treated, glaucoma can lead to blindness or significant loss of vision. There is therefore a continuing need for therapies which control the elevated intraocular pressure associated with glaucoma.
There are currently a number of drugs utilized in the treatment of glaucoma, including: miotics (e.g., pilocarpine, carbachol and acetylcholinesterase inhibitors); sympathomimetics (e.g., epinephrine and dipivalylepinephrine); alpha-2 agonists (e.g., para-amino clonidine); beta-blockers (e.g., betaxolol, levobunolol and timolol); and carbonic anhydrase inhibitors (e.g., acetazolamide, methazolamide and ethoxzolamide). Miotics and sympathomimetics are believed to lower IOP by increasing the outflow of aqueous humor through the trabecular meshwork, while beta-blockers, alpha-2 agonists and carbonic anhydrase inhibitors are believed to lower IOP by decreasing the formation of aqueous humor.
In addition, although they have not yet been approved for anti-glaucoma therapy, certain classes of prostaglandins and prostaglandin analogues (hereinafter collectively referred to as "prostaglandins") have been shown in various animal models and in some clinical studies to reduce intraocular pressure (IOP) to a greater extent than most currently used therapeutic agents. See, for example: U.S. Pat. Nos. 4,097,489 (Bundy), 4,599,353 (Bito), 4,994,274 (Chan et al.) and EP 289 349 (Ueno et al.). In contrast to the case with miotics, prostaglandins are believed to lower IOP by increasing the outflow of aqueous humor via the uveo-scleral route. In addition, prostaglandins may possibly have other effects in the eye, such as enhancing vascular support of ocular tissues; however, there is no understanding of that mechanism at this time.
All six types of therapeutic agents have potentially serious side effects: miotics such as pilocarpine can cause blurring of vision and other, visual side effects, which may lead either to decreased patient compliance or to termination of therapy; carbonic anhydrase inhibitors can also cause serious side effects which affect patient compliance and/or necessitate the withdrawal of treatment; at least one beta-blocker, timolol, has increasingly become associated with serious pulmonary side effects attributable to its effect on beta-2 receptors in pulmonary tissue; and prostaglandins often produce hyperemia and edema of the conjunctiva, resulting in redness and hyperesthesia of the eye, which may affect patient compliance. In addition to these side effects, a therapy regimen which includes the use of two or more pharmaceutical compositions containing drugs selected from two or more of the above-cited classes requires the patient to apply the, compositions to the affected eye(s) in separate, spaced dosages, several times per day. Patient compliance with such complicated dosage regimens can be very poor, particularly in elderly patients. Since the majority of glaucoma patients are elderly, this patient compliance problem is significant.
In light of the foregoing circumstances, it is clear that a need exists for new, more potent anti-glaucoma compositions which avoid or reduce the above-cited side effects, while increasing patient compliance. The present invention is directed to such compositions.